1.15: Urinary System
Learning Objectives
- Examine the anatomy of the urinary system
- Determine the main functions of the urinary system
- Differentiate urinary system medical terms and common abbreviations
- Recognize the medical specialties associated with the urinary system
- Discover common diseases, disorders, and procedures related to the urinary system
Urinary System Word Parts
Click on prefixes, combining forms, and suffixes to reveal a list of word parts to memorize for the urinary system.
Introduction to the Urinary System
The urinary system has roles you may be well aware of on a daily basis. Cleansing the blood and ridding the body of wastes probably come to mind. However, there are additional, equally important functions, played by the system. Take, for example, regulation of pH , a function shared with the lungs and the buffers in the blood. Additionally, the regulation of blood pressure is a role shared with the heart and blood vessels. What about regulating the concentration of solutes in the blood? Did you know that the kidney is important in determining the concentration of red blood cells? Eighty-five percent of the erythropoietin (EPO) produced to stimulate red blood cell production is produced in the kidneys. The kidneys also perform the final synthesis step of vitamin D production, converting calcidiol to calcitriol, the active form of vitamin D. If the kidneys fail, these functions are compromised or lost altogether, with devastating effects on homeostasis .
Watch this video:
Media 15.1. Urinary System, Part 1: Crash Course A&P #38 [Online video]. Copyright 2015 by CrashCourse .
Practice Medical Terms Related to the Urinary System
Anatomy (Structures) of the Urinary System
Kidneys
The kidneys lie on either side of the spine in the retroperitoneal space between the parietal peritoneum and the posterior abdominal wall, well protected by muscle, fat, and ribs. They are roughly the size of your fist. The male kidney is typically a bit larger than the female kidney. The kidneys are well vascularized, receiving about 25% of the cardiac output at rest. Figure 15.1 displays the location of the kidneys.
Kidneys’ Internal Structure
A frontal section through the kidney reveals an outer region called the renal cortex and an inner region called the medulla (see Figure 15.2 ). The renal columns are connective tissue extensions that radiate downward from the cortex through the medulla to separate the most characteristic features of the medulla, the renal pyramids and renal papillae. The papillae are bundles of collecting ducts that transport urine made by nephrons to the calyces of the kidney for excretion. The renal columns also serve to divide the kidney into 6 to 8 lobes and provide a supportive framework for vessels that enter and exit the cortex. The pyramids and renal columns taken together constitute the kidney lobes.
Did you know?
The right kidney is smaller than the left. It also sits slightly lower to make room for the liver located on the right side of your body.
Renal Hilum
The renal hilum is the entry and exit site for structures servicing the kidneys: vessels, nerves, lymphatics, and ureters. The medial-facing hila are tucked into the sweeping convex outline of the cortex. Emerging from the hilum is the renal pelvis, which is formed from the major and minor calyces in the kidney. The smooth muscle in the renal pelvis funnels urine via peristalsis into the ureter. The renal arteries form directly from the descending aorta, whereas the renal veins return cleansed blood directly to the inferior vena cava. The artery, vein, and renal pelvis are arranged in an anterior-to-posterior order.
Nephrons and Vessels
The renal artery first divides into segmental arteries, followed by further branching to form interlobar arteries that pass through the renal columns to reach the cortex (see Figure 15.3 ). The interlobar arteries, in turn, branch into arcuate arteries, cortical radiate arteries, and then into afferent arterioles. The afferent arterioles service about 1.3 million nephrons in each kidney.
Nephrons are the “functional units” of the kidney; they cleanse the blood and balance the constituents of the circulation. The afferent arterioles form a tuft of high-pressure capillaries about 200 µm in diameter, the glomerulus . The rest of the nephron consists of a continuous sophisticated tubule whose proximal end surrounds the glomerulus in an intimate embrace—this is Bowman’s capsule . The glomerulus and Bowman’s capsule together form the renal corpuscle . As mentioned earlier, these glomerular capillaries filter the blood based on particle size. After passing through the renal corpuscle, the capillaries form a second arteriole, the efferent arteriole (see Figure 15.4 ). These will next form a capillary network around the more distal portions of the nephron tubule, the peritubular capillaries and vasa recta , before returning to the venous system. As the glomerular filtrate progresses through the nephron, these capillary networks recover most of the solutes and water, and return them to the circulation. Since a capillary bed (the glomerulus) drains into a vessel that in turn forms a second capillary bed, the definition of a portal system is met. This is the only portal system in which an arteriole is found between the first and second capillary beds. Portal systems also link the hypothalamus to the anterior pituitary, and the blood vessels of the digestive viscera to the liver.
Ureters
The kidneys and ureters are completely retroperitoneal , and the bladder has a peritoneal covering only over the dome. As urine is formed, it drains into the calyces of the kidney, which merge to form the funnel-shaped renal pelvis in the hilum of each kidney. The hilum narrows to become the ureter of each kidney. As urine passes through the ureter, it does not passively drain into the bladder but rather is propelled by waves of peristalsis . The ureters are approximately 30 cm long. The inner mucosa is lined with transitional epithelium and scattered goblet cells that secrete protective mucus. The muscular layer of the ureter consists of longitudinal and circular smooth muscles that create the peristaltic contractions to move the urine into the bladder without the aid of gravity. Finally, a loose adventitial layer composed of collagen and fat anchors the ureters between the parietal peritoneum and the posterior abdominal wall.
Bladder
The urinary bladder collects urine from both ureters ( see Figure 15.5 ). The bladder lies anterior to the uterus in females, posterior to the pubic bone and anterior to the rectum. During late pregnancy, its capacity is reduced due to compression by the enlarging uterus, resulting in increased frequency of urination. In males, the anatomy is similar, minus the uterus, and with the addition of the prostate inferior to the bladder. The bladder is partially retroperitoneal (outside the peritoneal cavity) with its peritoneal-covered “dome” projecting into the abdomen when the bladder is distended with urine.
Urethra
The urethra transports urine from the bladder to the outside of the body for disposal. The urethra is the only urologic organ that shows any significant anatomic difference between males and females; all other urine transport structures are identical (see Figure 15.6 ).
The urethra in both males and females begins inferior and central to the two ureteral openings forming the three points of a triangular-shaped area at the base of the bladder called the trigone (Greek tri- = “triangle” and the root of the word “trigonometry”). The urethra tracks posterior and inferior to the pubic symphysis (see Figure 15.6 ). In both males and females, the proximal urethra is lined by transitional epithelium, whereas the terminal portion is a nonkeratinized, stratified squamous epithelium. In the male, pseudostratified columnar epithelium lines the urethra between these two cell types. Voiding is regulated by an involuntary autonomic nervous system-controlled internal urinary sphincter, consisting of smooth muscle and voluntary skeletal muscle that forms the external urinary sphincter below it.
Micturition Reflex
Micturition is a less-often used, but proper term for urination or voiding . It results from an interplay of involuntary and voluntary actions by the internal and external urethral sphincters. When bladder volume reaches about 150 mL, an urge to void is sensed but is easily overridden. Voluntary control of urination relies on consciously preventing relaxation of the external urethral sphincter to maintain urinary continence. As the bladder fills, subsequent urges become harder to ignore. Ultimately, voluntary constraint fails with resulting incontinence, which will occur as bladder volume approaches 300 to 400 ml.
- Normal micturition is a result of stretch receptors in the bladder wall that transmit nerve impulses to the sacral region of the spinal cord to generate a spinal reflex. The resulting parasympathetic neural outflow causes contraction of the detrusor muscle and relaxation of the involuntary internal urethral sphincter.
- At the same time, the spinal cord inhibits somatic motor neurons, resulting in the relaxation of the skeletal muscle of the external urethral sphincter .
- The micturition reflex is active in infants but with maturity, children learn to override the reflex by asserting external sphincter control, thereby delaying voiding (potty training). This reflex may be preserved even in the face of spinal cord injury that results in paraplegia or quadriplegia. However, relaxation of the external sphincter may not be possible in all cases, and therefore, periodic catheterization may be necessary for bladder emptying.
Nerves involved in the control of urination include the hypogastric, pelvic, and pudendal. Voluntary micturition requires an intact spinal cord and functional pudendal nerve arising from the sacral micturition center. Since the external urinary sphincter is voluntary skeletal muscle, actions by cholinergic neurons maintain contraction (and thereby continence) during filling of the bladder. At the same time, sympathetic nervous activity via the hypogastric nerves suppresses contraction of the detrusor muscle. With further bladder stretch, afferent signals traveling over sacral pelvic nerves activate parasympathetic neurons. This activates efferent neurons to release acetylcholine at the neuromuscular junctions, producing detrusor contraction and bladder emptying.
Did you know?
A healthy adult bladder can store up to 455 millilitres of urine for between two to five hours.
Concept Check
- Describe two organs or structures essential to the urinary system.
- Identify the structure within the kidneys which filters blood.
- Name a commonly used term for the micturition reflex.
Anatomy Labeling Activity
Physiology (Function) of the Urinary System
- Remove waste products and medicines from the body
- Balance the body’s fluids
- Balance a variety of electrolytes
- Release hormones to control blood pressure
- Release a hormone to control red blood cell production
- Help with bone health by controlling calcium and phosphorus
Having reviewed the anatomy of the urinary system now is the time to focus on physiology. You will discover that different parts of the nephron utilize specific processes to produce urine: filtration , reabsorption , and secretion . You will learn how each of these processes works and where they occur along the nephron and collecting ducts. The physiologic goal is to modify the composition of the plasma and, in doing so, produce the waste product urine.
Nephrons: The Functional Unit
Nephrons take a simple filtrate of the blood and modify it into urine. Many changes take place in the different parts of the nephron before urine is created for disposal. The term “forming urine” will be used hereafter to describe the filtrate as it is modified into true urine. The principal task of the nephron population is to balance the plasma to homeostatic set points and excrete potential toxins in the urine. They do this by accomplishing three principle functions—filtration, reabsorption, and secretion. They also have additional secondary functions that exert control in three areas: blood pressure (via the production of renin), red blood cell production (via the hormone EPO), and calcium absorption (via the conversion of calcidiol to calcitriol, the active form of vitamin D).
Loop of Henle
The descending and ascending portions of the loop of Henle (sometimes referred to as the nephron loop ) are, of course, just continuations of the same tubule. They run adjacent and parallel to each other after having made a hairpin turn at the deepest point of their descent. The descending loop of Henle consists of an initial short, thick portion and long, thin portion, whereas the ascending loop consists of an initial short, thin portion followed by a long, thick portion. The descending and ascending thin portions consist of simple squamous epithelium. Different portions of the loop have different permeabilities for solutes and water.
Collecting Ducts
The collecting ducts are continuous with the nephron but are not technically part of it. In fact, each duct collects filtrate from several nephrons for final modification. Collecting ducts merge as they descend deeper in the medulla to form about 30 terminal ducts, which empty at a papilla.
Glomerular Filtration Rate (GFR)
The volume of filtrate formed by both kidneys per minute is termed the glomerular filtration rate (GFR). The heart pumps about 5 L blood per min under resting conditions. Approximately 20% or one liter enters the kidneys to be filtered. On average, this liter results in the production of about 125 mL/min filtrate produced in men (range of 90 to 140 mL/min) and 105 mL/min filtrate produced in women (range of 80 to 125 mL/min). This amount equates to a volume of about 180 L/day in men and 150 L/day in women. Ninety-nine percent of this filtrate is returned to the circulation by reabsorption so that only about 1 to 2 liters of urine are produced per day.
GFR is influenced by the hydrostatic pressure and colloid osmotic pressure on either side of the capillary membrane of the glomerulus. Recall that filtration occurs as pressure forces fluid and solutes through a semipermeable barrier with the solute movement constrained by particle size. Hydrostatic pressure is the pressure produced by a fluid against a surface. If you have fluid on both sides of a barrier, both fluids exert pressure in opposing directions. The net fluid movement will be in the direction of the lower pressure. Osmosis is the movement of solvent (water) across a membrane that is impermeable to a solute in the solution. This creates osmotic pressure which will exist until the solute concentration is the same on both sides of a semipermeable membrane. As long as the concentration differs, water will move. Glomerular filtration occurs when glomerular hydrostatic pressure exceeds the luminal hydrostatic pressure of Bowman’s capsule. There is also an opposing force, the osmotic pressure, which is typically higher in the glomerular capillary. To understand why this is so, look more closely at the microenvironment on either side of the filtration membrane.
You will find osmotic pressure exerted by the solutes inside the lumen of the capillary as well as inside of Bowman’s capsule. Since the filtration membrane limits the size of particles crossing the membrane, the osmotic pressure inside the glomerular capillary is higher than the osmotic pressure in Bowman’s capsule. Recall that cells and the medium-to-large proteins cannot pass between the podocyte processes or through the fenestrations of the capillary endothelial cells. This means that red and white blood cells, platelets, albumins , and other proteins too large to pass through the filter remain in the capillary, creating an average colloid osmotic pressure of 30 mm Hg within the capillary. The absence of proteins in Bowman’s space (the lumen within Bowman’s capsule) results in an osmotic pressure near zero. Thus, the only pressure moving fluid across the capillary wall into the lumen of Bowman’s space is hydrostatic pressure. Hydrostatic (fluid) pressure is sufficient to push water through the membrane despite the osmotic pressure working against it. The sum of all of the influences, both osmotic and hydrostatic, results in a net filtration pressure (NFP) of about 10 mm Hg (see Figure 15.7 ).
A proper concentration of solutes in the blood is important in maintaining osmotic pressure both in the glomerulus and systemically. There are disorders in which too much protein passes through the filtration slits into the kidney filtrate. This excess protein in the filtrate leads to a deficiency of circulating plasma proteins. In turn, the presence of protein in the urine increases its osmolarity; this holds more water in the filtrate and results in an increase in urine volume. Because there is less circulating protein, principally albumin, the osmotic pressure of the blood falls. Less osmotic pressure pulling water into the capillaries tips the balance towards hydrostatic pressure, which tends to push it out of the capillaries. The net effect is that water is lost from the circulation to interstitial tissues and cells. This “plumps up” the tissues and cells, a condition termed systemic edema .
Reabsorption and Secretion
The renal corpuscle filters the blood to create a filtrate that differs from blood mainly in the absence of cells and large proteins. From this point to the ends of the collecting ducts, the filtrate or forming urine is undergoing modification through secretion and reabsorption before true urine is produced. Here, some substances are reabsorbed, whereas others are secreted. Note the use of the term “reabsorbed.” All of these substances were “absorbed” in the digestive tract—99% of the water and most of the solutes filtered by the nephron must be reabsorbed. Water and substances that are reabsorbed are returned to the circulation by the peritubular and vasa recta capillaries.
It is vital that the flow of blood through the kidney is at a suitable rate to allow for filtration. This rate determines how much solute is retained or discarded, how much water is retained or discarded, and ultimately, the osmolarity of blood and the blood pressure of the body.
Urinalysis
Urinalysis (urine analysis) often provides clues to renal disease. Normally, only traces of protein are found in urine, and when higher amounts are found, damage to the glomeruli is the likely basis. Unusually large quantities of urine may point to diseases like diabetes mellitus or hypothalamic tumors that cause diabetes insipidus. The color of urine is determined mostly by the breakdown products of red blood cell destruction (see Figure 15.8 ). The “heme” of hemoglobin is converted by the liver into water-soluble forms that can be excreted into the bile and indirectly into the urine. This yellow pigment is urochrome. Urine color may also be affected by certain foods like beets, berries, and fava beans. A kidney stone or a cancer of the urinary system may produce sufficient bleeding to manifest as pink or even bright red urine. Diseases of the liver or obstructions of bile drainage from the liver impart a dark “tea” or “cola” hue to the urine. Dehydration produces darker, concentrated urine that may also possess the slight odor of ammonia . Most of the ammonia produced from protein breakdown is converted into urea by the liver, so ammonia is rarely detected in fresh urine. The strong ammonia odor you may detect in bathrooms or alleys is due to the breakdown of urea into ammonia by bacteria in the environment. About one in five people detect a distinctive odor in their urine after consuming asparagus; other foods such as onions, garlic, and fish can impart their own aromas. These food-caused odors are harmless.
Urine volume varies considerably. The normal range is one to two liters per day. The kidneys must produce a minimum urine volume of about 500 mL/day to rid the body of wastes. Output below this level may be caused by severe dehydration or renal disease and is termed oliguria . The virtual absence of urine production is termed anuria . Excessive urine production is polyuria , which may be due to diabetes mellitus or diabetes insipidus. In diabetes mellitus, blood glucose levels exceed the number of available sodium-glucose transporters in the kidney, and glucose appears in the urine. The osmotic nature of glucose attracts water, leading to its loss in the urine. In the case of diabetes insipidus, insufficient pituitary antidiuretic hormone (ADH) release or insufficient numbers of ADH receptors in the collecting ducts means that too few water channels are inserted into the cell membranes that line the collecting ducts of the kidney. Insufficient numbers of water channels (aquaporins) reduce water absorption, resulting in high volumes of very dilute urine.
Concept Check
- Contrast the following terms: oliguria , anuria and polyuria . What are the differences between these terms as they describe urinary output?
- Explain how urine color varies based on food consumed and/or hydration levels.
Endocrine Urinary Function
Several hormones have specific, important roles in regulating kidney function. They act to stimulate or inhibit blood flow. Some of these are endocrine, acting from a distance, whereas others are paracrine, acting locally.
Renin–Angiotensin–Aldosterone
Renin is an enzyme that is produced by the granular cells of the afferent arteriole. It enzymatically converts angiotensinogen (made by the liver, freely circulating) into angiotensin I. Its release is stimulated by prostaglandins to decrease extracellular fluid volume.
Angiotensin II is a potent vasoconstrictor that plays an immediate role in the regulation of blood pressure. It acts systemically to cause vasoconstriction as well as constriction of both the afferent and efferent arterioles of the glomerulus. In instances of blood loss or dehydration, it reduces both GFR and renal blood flow, thereby limiting fluid loss and preserving blood volume. Its release is usually stimulated by decreases in blood pressure, and so the preservation of adequate blood pressure is its primary role.
Aldosterone, often called the “salt-retaining hormone,” is released from the adrenal cortex in response to angiotensin II or directly in response to increased plasma potassium. It promotes sodium reabsorption by the nephron, promoting the retention of water.
Antidiuretic Hormone (ADH)
Diuretics are drugs that can increase water loss by interfering with the recapture of solutes and water from the forming urine. They are often prescribed to lower blood pressure. Coffee, tea, and alcoholic beverages are familiar diuretics. ADH, released by the posterior pituitary, works to do the exact opposite. It promotes the recovery of water, decreases urine volume, and maintains plasma osmolarity and blood pressure. It does so by stimulating the movement of aquaporin proteins into the apical cell membrane of principal cells of the collecting ducts to form water channels, allowing the transcellular movement of water from the lumen of the collecting duct into the interstitial space in the medulla of the kidney by osmosis. From there, it enters the vasa recta capillaries to return to the circulation. Water is attracted by the high osmotic environment of the deep kidney medulla.
Parathyroid Hormone
Parathyroid hormone (PTH) is produced by the parathyroid glands in response to decreased circulating calcium levels.
Maintaining Homeostasis
Homeostasis requires that volume and osmolarity be preserved. Blood volume is important in maintaining sufficient blood pressure, and there are nonrenal mechanisms involved in its preservation, including vasoconstriction, which can act within seconds of a drop in pressure. Thirst mechanisms are also activated to promote the consumption of water lost through respiration, evaporation, or urination. Hormonal mechanisms are activated to recover volume while maintaining a normal osmotic environment. These mechanisms act principally on the kidney.
Diuretics and Fluid Volume
A diuretic is a compound that increases urine volume. Three familiar drinks contain diuretic compounds: coffee, tea, and alcohol. The caffeine in coffee and tea works by promoting vasodilation in the nephron, which increases GFR. Alcohol increases GFR by inhibiting ADH release from the posterior pituitary, resulting in less water recovery by the collecting duct. In cases of high blood pressure, diuretics may be prescribed to reduce blood volume and, thereby, reduce blood pressure. The most frequently prescribed anti-hypertensive diuretic is hydrochlorothiazide.
Regulation of Nitrogen Wastes
Nitrogen wastes are produced by the breakdown of proteins during normal metabolism . Proteins are broken down into amino acids, which in turn are deaminated by having their nitrogen groups removed. Deamination converts the amino (NH2) groups into ammonia (NH3), ammonium ion (NH4+), urea, or uric acid ( Figure 15.9 ). Ammonia is extremely toxic, so most of it is very rapidly converted into urea in the liver. Human urinary wastes typically contain primarily urea with small amounts of ammonium and very little uric acid.
Elimination of Drugs and Hormones
Water-soluble drugs may be excreted in the urine and are influenced by one or all of the following processes: glomerular filtration, tubular secretion, or tubular reabsorption. Drugs that are structurally small can be filtered by the glomerulus with the filtrate. Large drug molecules such as heparin or those that are bound to plasma proteins cannot be filtered and are not readily eliminated. Some drugs can be eliminated by carrier proteins that enable secretion of the drug into the tubule lumen. There are specific carriers that eliminate basic (such as dopamine or histamine) or acidic drugs (such as penicillin or indomethacin). As is the case with other substances, drugs may be both filtered and reabsorbed passively along a concentration gradient.
Watch this video:
Media 15.2. Urinary System, Part 2: Crash Course A&P #39 [Online video]. Copyright 2015 by CrashCourse .
Practice Terms Related to the Urinary System
Common Abbreviations for the Urinary System
Many terms and phrases related to the urinary system are abbreviated. Learn these common abbreviations by expanding the list below.
Diseases and Disorders of the Urinary System
Diabetic Nephropathy
Diabetic nephropathy impacts the kidneys as a result of having diabetes mellitus type 1 or 2. Higher levels of blood sugar can lead to high blood pressure and this additional pressure exerted on the kidneys causes destruction of the small filtering structures within the kidney (Varghese & Jialal, 2021). To learn more, visit the Mayo Clinic’s web page on diabetic nephropathy .
Glomerulonephritis
Glomerulonephritis refers to acute or chronic nephritis that involves inflammation of the capillaries of the renal glomeruli. It is characterized by blood or protein in the urine and edema. If untreated, it could lead to kidney failure. Glomerulonephritis may be caused by a variety of infections and immune conditions, as a result of genetic defects, or by unknown causes (Genetic and Rare Diseases Information Center, 2012). For more information, visit the Genetic and Rare Diseases Information Center’s web page on glomerulonephritis .
Hydronephrosis
Hydronephrosis is a condition whereby the kidneys begin to swell because of the retention of urine. Several conditions can cause hydronephrosis, such as a kidney stone or pregnancy. Treatment will vary, depending on the cause (Thotakura & Anjum, 2021). To learn more, visit the Cleveland Clinic’s web page on hydronephrosis.
Polycystic Kidney Disease
Polycystic kidney disease (PKD) is a genetic disorder whereby cysts grow inside the kidneys. The kidneys enlarge from the cystic collections, and damage to the filtering structures of the kidneys can occur. As the disease progresses, it may lead to kidney failure (National Institute of Diabetes and Digestive and Kidney Diseases, n.d.-a). To learn more, visit the National Institute of Diabetes and Digestive and Kidney Diseases’ web page on polycystic kidney disease .
Renal Cell Carcinoma
Renal cell carcinoma is a cancer occurring in the kidney tubes where urine is produced or collected. Signs and symptoms may include blood in the urine and the presence of a lump in the abdomen. Risk factors include smoking and the long-term misuse of pain medicine (National Cancer Institute, 2020). For more information, visit the National Cancer Institute’s web page on renal cell carcinoma .
Renal Failure
Renal failure occurs when kidneys become unable to filter waste products from blood. When kidneys stop filtering, high levels of waste may build. Renal failure may be acute (sudden onset) or chronic (gradual onset) (Bindroo et al., 2021). For more information, visit the Cleveland Clinic’s web page on renal failure .
Cystitis
Cystitis is inflammation of the urinary bladder, often caused by an infection. A chronic form of this condition is known as interstitial cystitis. Signs and symptoms of cystitis include bladder pressure, voiding frequently, and abdominal pain (Centers for Disease Control and Prevention, n.d.; Li & Leslie, 2021). To learn more, visit the Mayo Clinic’s web page on cystitis.
Urinary Tract Infection
A urinary tract infection (UTI) is an infection caused by bacteria. The exact type of bacterial growth is determined by conducting a urine culture. Signs and symptoms include a burning sensation during urination and voiding frequently (National Institute of Diabetes and Digestive and Kidney Diseases, n.d.-b). For more information, visit the National Institute of Diabetes and Digestive and Kidney Diseases’ web page on urinary tract infections .
Urinary Incontinence
Urinary incontinence is a loss of bladder control. Those afflicted with the condition will experience urine leakage from the bladder. Urinary incontinence may be related to another health issue, such as prostate problems, or it may be the result of weakened urinary tract muscles (National Institute of Diabetes and Digestive and Kidney Diseases, n.d.-c). For more information, visit the National Institute of Diabetes and Digestive and Kidney Diseases’ web page on bladder incontinence .
Medical Terms in Context
Medical Specialties and Procedures Related to the Urinary System
Urology is a specialty that focuses on the diagnosis, treatment, and surgical repair of the urinary tract. To learn more about urology as a specialty, visit the American College of Surgeons’ web page.
Urologist
A urologist is a medical specialist involved in the diagnosis and treatment of urinary and male genitourinary system conditions, disorders, and diseases (National Cancer Institute, n.d.-a). To learn more about what urologists do and how to become one, visit the Cleveland Clinic’s web page about the specialty .
Procedures and Testing
Urinalysis
A urinalysis is the physical, chemical, and microscopic examination of urine. This test detects and measures several substances in the urine such as products of normal and abnormal metabolism and bacteria (Queremel Milani & Jialal, 2021). To learn more, visit the Mayo Clinic’s web page on urinalysis .
Urine Culture and Sensitivity
A urine culture is a test that can detect and identify bacteria in the urine, which may be causing a urinary tract infection (UTI). If harmful bacteria is found, a sensitivity report is generated. A sensitivity test indicates which antibiotics will be effective in treating the infection (Sinawe & Casadesus, 2021; MedlinePlus, 2021). For more information, visit MedlinePlus’ web page on urine cultures .
24-Hour Urinalysis
A 24-hour urinalysis is a test whereby all urinary output is collected over a 24-hour period of time. The analysis of urinary output over this extended period of time provides a greater indication of normal or abnormal kidney function (Corder et al., 2021). For more information, visit Johns Hopkins Medicine’s web page on 24-hour urine collection .
CT Scan of Kidney
Computed tomography is a diagnostic imaging procedure that uses a combination of x-rays and computer technology to produce a variety of images (National Cancer Institute, n.d.-b). It provides detailed images of the kidney so that healthcare professionals can diagnose disease, obstructions, and other kidney conditions. To learn more, visit Johns Hopkins Medicine’s page on computed tomography scan of the kidney.
Cystoscopy
A cystoscopy is a procedure allowing a physician to view the bladder and urethra. The procedure involves the use of a cystoscope, a long tube-like instrument that has a camera and light at the end. The camera’s images are transmitted to a computer, where the urologist can determine whether the patient has bladder stones, cancer, or other urinary tract problems (National Institute of Diabetes and Digestive and Kidney Diseases, n.d.-d). For more information, view the National Institute of Diabetes and Digestive and Kidney Diseases’ web page on cystoscopy .
Dialysis
Dialysis is a treatment that removes waste products from the blood when the kidneys are not fully functioning. This type of therapy is available at home, in a hospital, or clinic. There are two main types: peritoneal dialysis and hemodialysis (National Institute of Diabetes and Digestive and Kidney Diseases, n.d.-e). To learn more, visit the National Institute of Diabetes and Digestive and Kidney Diseases’ web page on kidney failure treatment options .
Intravenous Pyelogram
An intravenous pyelogram (IVP) is a specialized x-ray designed to produce views of the entire urinary tract. Contrast dye is used to produce clear x-ray images. The x-rays can show how well the urinary tract is functioning and identify any blockages (MedlinePlus, 2020). For more information, visit MedlinePlus’ web page on intravenous pyelogram .
Kidney Scan
A kidney scan is an imaging test which views the kidneys. It is considered a nuclear imaging test as it uses radioactive tracers to evaluate kidney function. A kidney scan may be performed if the patient is allergic to the contrast material used with CT or MRI tests (Banker et al., 2021). For more information, visit MedlinePlus’ web page on renal scans .
Kidney Transplant
When a patient experiences kidney failure, a healthy kidney can be surgically transplanted from a donor to the patient. The donor may be living or recently deceased. Patients may have to wait for many years before a kidney is available and may have to go on dialysis in the meantime (National Institute of Diabetes and Digestive and Kidney Diseases, n.d.-f). For more information, visit the National Institute of Diabetes and Digestive and Kidney Diseases’ web page on kidney transplant .
Urinary System Vocabulary
Adventitial : The outermost layer of organs, blood vessels, and other structures in the body.
Albuminuria : Albumin in the urine.
Anuria : The absence of urine production.
Autonomic : Involuntary or unconscious.
Azotemia : Urea in the blood.
Cystectomy : Excision of all or part of the bladder to remove a cyst.
Cystitis : Inflammation of the lining of the bladder.
Cystocele : A condition in which weakened pelvic muscles cause the bladder from its normal position.
Cystography : Radiographic imaging of the bladder.
Cystoscope : A thin, tube-like instrument used to look inside the bladder and urethra.
Cystoscopy : Examination of the bladder and urethra using a cystoscope, inserted into the urethra.
Cystostomy : Creation of an artificial opening into the bladder.
Cystotomy : Incision into the bladder.
Deamination: The removal of an amino group from a molecule.
Detrusor : A muscle which forms a layer of the wall of the bladder.
Diuresis : Excess production of urine.
Dysuria : Painful urination.
Enuresis : Involuntary urination.
Excretion : To get rid of waste material from the blood, tissues, or organs by a normal discharge (such as sweat, urine, or stool).
Glomerulonephritis : A condition in which the tissues in the kidney become inflamed and have problems filtering waste from the blood.
Glycosuria : Presence of glucose in the urine.
Hematuria : Blood in the urine.
Homeostasis : The state of steady internal conditions maintained by living things.
Hydronephrosis : Abnormal enlargement of a kidney, which may be caused by blockage of the ureter (such as by a kidney stone) or chronic kidney disease that prevents urine from draining into the bladder.
Hydrostatic: Relating to the equilibrium of liquids and the pressure exerted by liquid at rest.
Hypothalamus : A region of the forebrain below the thalamus; has function in both the autonomic and endocrine systems and regulates homeostasis.
Incontinence : Loss of ability to control micturition (urination).
Lethargy : A condition marked by drowsiness and an unusual lack of energy and mental alertness.
Micturition : Also called urination or voiding.
Lithotripsy : The destruction of a calculus (stone) of the kidney, ureter, bladder, or gallbladder by physical forces.
Mitochondria : A membranous, bean-shaped organelle that is the “energy transformer” of the cell.
Nephrectomy : Excision of all or part of the kidney.
Nephritis : A condition in which the tissues in the kidney become inflamed and have problems filtering waste from the blood.
Nephrolithiasis : Formation of stone(s) in the kidney.
Nephrolithotomy : Incision into the kidney to remove stone(s).
Nephrologist : A doctor who has special training in diagnosing and treating kidney disease.
Nephrology : A subspecialty of internal medicine concerned with the anatomy, physiology, and pathology of the kidney.
Nephrostomy : Surgery to make an opening from the outside of the body to the renal pelvis.
Nocturia : Frequent urination at night that interrupts sleep.
Oliguria : Below normal urine production of 400–500 mL/day.
Osmosis : A process by which molecules of a solvent tend to pass through a membrane from a less concentrated solution into a more concentrated one.
pH : A measure of how acidic or alkaline a substance is, as determined by the number of free hydrogen ions in the substance.
Polyuria : Excessive urine production.
Prostaglandins: Signaling molecules derived from unsaturated fatty acids with hormone-like effects.
Pseudostratified : Tissue with a single layer of irregularly shaped cells that give the appearance of more than one layer.
Pyelitis : Inflammation of the renal pelvis and kidney calices.
Pyelonephritis : Inflammation of the nephrons, renal pelvis, and kidney calices.
Pyuria : The presence of white blood cells in the urine.
Solutes: The minor component in a solution.
Stricture : Abnormal narrowing.
Ureterocele : A cystic dilatation of the end of a ureter.
Ureterolithiasis : Formation of stone(s) in the ureter.
Ureteroscopy : Examination of the inside of the kidney and ureter, using a ureteroscope.
Ureterostomy : Creation of an artificial opening into the ureter.
Urinal : Receptacle used for the collection of urine.
Urinary : Pertaining to urine or the organs of the body that produce and get rid of urine.
Urologist : A doctor who has special training in diagnosing and treating diseases of the urinary organs in females and the urinary and reproductive organs in males.
Urology : A surgical specialty concerned with the study, diagnosis, and treatment of diseases of the urinary tract in both sexes, and the genital tract in the male.
Voiding : Also known as urination or micturition.
Test Yourself
References
Banker, H., Sheffield, E. G., & Cohen, H. L. (2021). Nuclear renal scan. In StatPearls [Internet]. https://www.ncbi.nlm.nih.gov/books/NBK562236/
Bindroo, S., Quintanilla Rodriguez, B.S., & Challa, H. J. (2021). Renal failure. In StatPearls [Internet] . https://www.ncbi.nlm.nih.gov/books/NBK519012/
Centers for Disease Control and Prevention. (n.d.). Interstitial cystitis. https://www.cdc.gov/ic/index.html
Corder, C. J., Rathi, B. M., Sharif, S., & Leslie, S. W. (2021). 24-hour urine collection. In StatPearls [Internet] . https://www.ncbi.nlm.nih.gov/books/NBK482482/
[CrashCourse]. (2015, October 12). Urinary system, part 1: Crash course A&P #38 [Video]. YouTube. https://www.youtube.com/watch?v=l128tW1H5a8
CrashCourse. (2015, June 22). Urinary system, part 2: Crash course A&P #39 [Video]. YouTube. https://youtu.be/DlqyyyvTI3k
Genetic and Rare Diseases Information Center. (2012). Glomerulonephritis . National Institutes of Health, U.S. Department of Health and Human Services. https://rarediseases.info.nih.gov/diseases/6516/glomerulonephritis
Li, R., & Leslie, S. W. (2021). Cystitis. In StatPearls [Internet] . https://www.ncbi.nlm.nih.gov/books/NBK482435/
MedlinePlus. (2021). Antibiotic sensitivity test . U.S. National Library of Medicine. https://medlineplus.gov/lab-tests/antibiotic-sensitivity-test/
MedlinePlus. (2020). Intravenous pyelogram . U.S. National Library of Medicine. https://medlineplus.gov/lab-tests/intravenous-pyelogram-ivp/
National Cancer Institute. (n.d.-a). Definition of urologist . National Institutes of Health, U.S. Department of Health and Human Services. https://www.cancer.gov/publications/dictionaries/cancer-terms/def/urologist
National Cancer Institute. (n.d.-b). Computed tomography (CT) scans and cancer . National Institutes of Health, U.S. Department of Health and Human Services. https://www.cancer.gov/about-cancer/diagnosis-staging/ct-scans-fact-sheet
National Cancer Institute. (2020). Renal cell cancer treatment (PDQ®) – Patient version . National Institutes of Health, U.S. Department of Health and Human Services. https://www.cancer.gov/types/kidney/patient/kidney-treatment-pdq
National Institute of Diabetes and Digestive and Kidney Diseases. (n.d.-a). P olycystic kidney disease? National Institutes of Health, U.S. Department of Health and Human Services. https://www.niddk.nih.gov/health-information/kidney-disease/polycystic-kidney-disease/all-content
National Institute of Diabetes and Digestive and Kidney Diseases. (n.d.-b). Bladder infection (urinary tract infection) in adults . National Institutes of Health, U.S. Department of Health and Human Services. https://www.niddk.nih.gov/health-information/urologic-diseases/bladder-infection-uti-in-adults/all-content
National Institute of Diabetes and Digestive and Kidney Diseases. (n.d.-c). Urinary incontinence . National Institutes of Health, U.S. Department of Health and Human Services. https://www.niddk.nih.gov/health-information/urologic-diseases/bladder-control-problems/all-content
National Institute of Diabetes and Digestive and Kidney Diseases. (n.d.-d). Cystoscopy & ureteroscopy . National Institutes of Health, U.S. Department of Health and Human Services. https://www.niddk.nih.gov/health-information/diagnostic-tests/cystoscopy-ureteroscopy
National Institute of Diabetes and Digestive and Kidney Diseases. (n.d.-e). Choosing a treatment for kidney failure . National Institutes of Health, U.S. Department of Health and Human Services. https://www.niddk.nih.gov/health-information/kidney-disease/kidney-failure/choosing-treatment
National Institute of Diabetes and Digestive and Kidney Diseases. (n.d.-f). Kidney transplant . National Institutes of Health, U.S. Department of Health and Human Services. https://www.niddk.nih.gov/health-information/kidney-disease/kidney-failure/kidney-transplant
Queremel Milani, D. A., & Jialal, I. (2021). Urinalysis. In StatPearls [Internet] . https://www.ncbi.nlm.nih.gov/books/NBK557685/
Sinawe, H., Casadesus, D. (2021). Urine culture. In StatPearls [Internet] . https://www.ncbi.nlm.nih.gov/books/NBK557569/
Thotakura, R., & Anjum, F. (2021). Hydronephrosis and hydroureter. In StatPearls [Internet] . https://www.ncbi.nlm.nih.gov/books/NBK563217/
Varghese, R. T., & Jialal, I. (2021). Diabetic nephropathy. In StatPearls [Internet] . https://www.ncbi.nlm.nih.gov/books/NBK534200/
Image Descriptions
Figure 15.1 image description: Diagram of a human torso showing the location of the kidneys within the torso. Callouts identify the liver, kidney, ureter, and 12th rib. [Return to Figure 15.1].
Figure 15.2 image description: The left panel of this figure shows the location of the kidneys in the abdomen. The right panel shows the cross-section of the kidney. [Return to Figure 15.2].
Figure 15.3 image description: This figure shows the network of blood vessels and the blood flow in the kidneys. Callouts identify the process as follows: renal artery, segmental artery, interlobar artery, arcuate artery, interlobular artery, afferent arteriole, glomerulus, efferent arteriole, peritubular capillaries, interlobular vein, arcuate vein, interlobar vein, and renal vein. [Return to Figure 15.3].
Figure 15.4 image description: This image shows the blood vessels and the direction of blood flow in the nephron. Callouts identify the process as involving the following structures: interlobular artery, afferent arteriole, efferent arteriole, glomerular capsule, proximal convoluted tubule, venule, interlobular vein, loop of the nephron, and peritubular capillary network. Urine then flows into the renal papilla. [Return to Figure 15.4].
Figure 15.5 image description: The left panel of this figure shows the cross-section of the bladder and the major parts are labeled. The right panel shows a micrograph of the bladder. [Return to Figure 15.5].
Figure 15.6 image description: Diagrams of the (a) female and (b) male genitalia highlighting the respective urethras. [Return to Figure 15.6].
Figure 15.7 image description: This figure shows the different pressures acting across the glomerulus including blood hydrostatic pressure, blood colloid osmotic pressure, capsular hydrostatic pressure. [Return to Figure 15.7].
Figure 15.8 image description: This color chart shows 8 different shades of yellow and associates each shade with stages of hydration (lightest 3 shades) or dehydration (remaining 5 darker shades). [Return to Figure 15.8].
Figure 15.9 image description: This figure shows the chemical structure of ammonia, urea, and uric acid. [Return to Figure 15.9].
Unless otherwise indicated, this chapter contains material adapted from Anatomy and Physiology (on OpenStax ), by Betts et al. and is used under a CC BY 4.0 international license . Download and access this book for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction .